The present invention relates to a control valve for controlling the displacement of a variable displacement compressor, which is used, for example, in a vehicle air conditioner.
A typical vehicle air conditioner includes a condenser, an expansion valve, as a depressurizing device, an evaporator, and a compressor. The compressor draws refrigerant gas from the evaporator, compresses it, and then discharges the compressed gas to the condenser. The evaporator transfers heat between the refrigerant flowing in the refrigerant circuit and air in the vehicle. In accordance with the cooling load, the heat of air passing near the evaporator is transferred to the refrigerant flowing in the evaporator. The pressure of the refrigerant gas in the vicinity of the outlet of the evaporator reflects the cooling load.
A swash plate type variable displacement compressor for such an air conditioner is provided with a displacement control system for steering the pressure near the outlet of the evaporator (suction pressure Ps) to a target suction pressure. The displacement control system controls the discharge displacement of the compressor by referring to the suction pressure Ps to obtain a flow rate that corresponds to the cooling load.
However, in a compressor that refers the suction pressure Ps to control the refrigerant flow rate, when the flow rate of refrigerant in the refrigerant circuit changes in accordance with a change of the engine speed, the displacement of the compressor does not always change immediately in response to the change of the flow rate. For example, if the engine speed increases and the flow rate of refrigerant increases accordingly when the thermal load on the evaporator is great, the compressor displacement does not start decreasing until the actual auction pressure falls below the target suction pressure. As the engine speed increases, the power required for operating the compressor increases, which lowers the fuel economy.
Accordingly, it is an objective of the present invention to provide a control valve that quickly changes the displacement of a variable displacement compressor regardless of the thermal load on an evaporator.
To attain the above object, the present invention provides a control valve used for a variable displacement compressor installed in a refrigerant circuit of a vehicle air conditioner. The compressor varies the displacement in accordance with the pressure in a crank chamber. The compressor has a control passage, which connects the crank chamber to a pressure zone in which the pressure is different from the pressure of the crank chamber. The control valve comprise a valve housing. A valve chamber is defined in the valve housing. A valve body, which is accommodated in the valve chamber adjusts the opening size of the control housing. A pressure sensing member, which separates the pressure sensing chamber into a first pressure chamber and a second pressure chamber. The pressure at a first location in the refrigerant circuit is applied to the first pressure chamber. The pressure at a second location in the refrigerant circuit, which is downstream of the first location, is applied to the second pressure chamber. The pressure sensing member moves the valve body in accordance with the pressure difference between the first pressure chamber and the second pressure chamber such that the displacement of the compressor is varied to counter changes of the pressure difference. At least one of the first pressure chamber and the second pressure chamber forms a part of the refrigerant circuit.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principal of the invention.